Verification and Validation of Supersonic Flutter of Rudder Model for Experiment

The abrupt and explosive nature of flutter is a dangerous failure mode, which is closely related to the structural modes. In this work, the principal goal of the study is to produce the model, which is used very accurately for flutter predictions. Mode correctness of the model can correct the test deflects by the optimization technique----Sequential Quadratic Programming (SQP). The optimization of two finite element models for two flight conditions, transonic and supersonic speeds, had the different objectives which were defined by the nonlinear and linear eigenvector errors. The first and second frequencies were taken as constraints. And the stiffness of the rotation shaft was also restricted to some limits. The stiffness of the rudder axle was defined as design variables. Experiments were performed for considering springs both in plunge and in torsion of the rudder shaft. When the comparison between experimental information and analyzed calculations is described, generally excellent agreement is obtained between experimental and calculated results, and aeroelastic instability is predicted that agrees with experimental observations. Comments are also given concerning improvements of the flutter speed to be made to the model with changing stiffness of the rudder axle. Most importantly, V&V Method is used to provide the confidence in the results from simulation in this paper. Firstly, it introduces experimental data from Ground Vibration Test to build up or modify the Finite Element Model, during the Verification phase, which makes simulated models closer to the real world and guarantees satisfaction of final computed results to requirements, such as airworthiness. Secondly, the flutter consequence is validated by wind tunnel test. These enhancements could find potential applications in industrial problems.

Supersonic Aerodynamic Instability Characteristics of Bidirectional Porous Functionally Graded Panel

The objective to alleviate the detrimental effects of supersonic flutter of aerospace structures necessitates the development of advanced composite materials. Porous functionally graded materials are viable alternatives to replace the metal/alloys used for critical components. The present work investigates the supersonic flutter characteristics of hinged-hinged panel for the porosity grading across the thickness and/or along the streamwise direction. Also, the possibility to alleviate the detrimental effects is investigated through the study of influence of streamwise and spanwise curvatures. A geometrically nonlinear finite element model of panel is derived using first-order shear deformation theory while the aerodynamic pressure on panel is accounted using the first-order piston theory. The results revealed that symmetric distribution of porosity with minimum porosity at the midspan and maximum porosity at core displays the better performance. Porosity and streamwise curvature reduces critical aerodynamic pressure and enhances flutter amplitude. For higher streamwise curvatures/porosity, panel undergoes snap-through buckling resulting in complex vibrations. Whereas the spanwise curvature substantially enhance the critical dynamic pressure thereby eliminates complex oscillations and snap-through. But moderately increases the flutter amplitude and frequency beyond its critical aerodynamic pressure. At higher spanwise curvatures, the effectiveness of bidirectional grading decreases making its through-thickness grading as dominant.

Effects of Material Constructions on Supersonic Flutter Characteristics for Composite Rectangular Plates Reinforced with Carbon Nano-structures

In this paper effects of material constructions on natural frequencies and critical aerodynamic pressures are investigated. It is assumed that the rectangular plate is made of a polymeric matrix reinforced with graphene nanoplatelets or carbon nanotubes. A general closed analytical method of solution is presented. It is demonstrated that three parameters define entirely the location of the critical flutter pressure. The influence of material properties and transverse shear effects is characterized by a set of multipliers. They can be easily adopted in design procedures.